U.S. patent number 7,978,255 [Application Number 12/285,789] was granted by the patent office on 2011-07-12 for solid-state image sensor and image-capturing device.
This patent grant is currently assigned to Nikon Corporation. Invention is credited to Satoshi Suzuki.
United States Patent |
7,978,255 |
Suzuki |
July 12, 2011 |
Solid-state image sensor and image-capturing device
Abstract
A solid-state image sensor includes: a plurality of
image-capturing pixels, each equipped with a first micro-lens used
to condense light; and a plurality of focus detection pixels
engaged in focus detection, each equipped with a second micro-lens
used to condense light; the plurality of image-capturing pixels and
the plurality of focus detection pixels being disposed in a
two-dimensional array. The first micro-lens and the second
micro-lens are formed so that a light condensing position at which
light is condensed via the second micro-lens is set further toward
a micro-lens side than the light condensing position at which light
is condensed via the first micro-lens.
Inventors: |
Suzuki; Satoshi (Tokyo,
JP) |
Assignee: |
Nikon Corporation (Tokyo,
JP)
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Family
ID: |
40623340 |
Appl.
No.: |
12/285,789 |
Filed: |
October 14, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090122171 A1 |
May 14, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60960747 |
Oct 11, 2007 |
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Foreign Application Priority Data
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Oct 11, 2007 [JP] |
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2007-265388 |
Dec 28, 2007 [JP] |
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2007-339754 |
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Current U.S.
Class: |
348/350; 348/340;
359/626; 250/208.1; 348/315; 348/294; 348/345; 348/222.1 |
Current CPC
Class: |
H04N
5/36961 (20180801); H04N 5/232122 (20180801) |
Current International
Class: |
H04N
5/232 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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B2-2604890 |
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Apr 1997 |
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JP |
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B2-2776810 |
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Jul 1998 |
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JP |
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2003244712 |
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Aug 2003 |
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JP |
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A-2003-244712 |
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Aug 2003 |
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JP |
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A-2006-261929 |
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Sep 2006 |
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JP |
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Primary Examiner: Chan; Jason
Assistant Examiner: Kao; Yih-Sien
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A solid-state image sensor, comprising: a plurality of
image-capturing pixels, each equipped with a first micro-lens used
to condense light; and a plurality of focus detection pixels
engaged in focus detection, each equipped with a second micro-lens
used to condense light; the plurality of image-capturing pixels and
the plurality of focus detection pixels being disposed in a
two-dimensional array, wherein: the first micro-lens and the second
micro-lens are formed so that a light condensing position at which
light is condensed via the second micro-lens is set further toward
a micro-lens side than the light condensing position at which light
is condensed via the first micro-lens.
2. A solid-state image sensor according to claim 1, wherein: the
plurality of image-capturing pixels and the plurality of focus
detection pixels each include a photoelectric converter; the
photoelectric converter of each of the plurality of image-capturing
pixels and the photoelectric converter of each of the plurality of
focus detection pixels are disposed on a single plane; and the
first micro-lens and the second micro-lens are disposed on a single
plane.
3. A solid-state image sensor according to claim 1, wherein: the
plurality of image-capturing pixels and the plurality of focus
detection pixels each include a photoelectric converter; the
plurality of focus detection pixels each include a light shield
member with an opening formed therein; the light shield member is
disposed between the photoelectric converter and the second
micro-lens; and the light condensing position at which light is
condensed via the second micro-lens is set on a plane on which the
light shield member is disposed.
4. A solid-state image sensor according to claim 1, wherein: the
light condensing position of the second micro-lens is adjusted
toward the micro-lens side relative to the light condensing
position of the first micro-lens by setting a greater curvature for
a lens surface of the second micro-lens than a curvature of a lens
surface of the first micro-lens.
5. A solid-state image sensor according to claim 4, wherein: the
greater curvature of the lens surface of the second micro-lens than
the curvature of the lens surface of the first micro-lens is set by
setting a lens thickness of the second micro-lens to be greater
than a lens thickness of the first micro-lens.
6. A solid-state image sensor according to claim 5, wherein:
provided that a uniform lens diameter is assumed, a ratio of the
lens thickness of the second micro-lens and the lens thickness of
the first micro-lens is set equal to or greater than 1.1 and less
than 1.4.
7. A solid-state image sensor according to claim 4, wherein: the
greater curvature of the lens surface of the second micro-lens than
the curvature of the lens surface of the first micro-lens is set by
setting a lens diameter of the second micro-lens to be smaller than
a lens diameter of the first micro-lens.
8. A solid-state image sensor according to claim 7, wherein:
provided that a uniform lens thickness is assumed, a ratio of the
lens diameter of the second micro-lens and the lens diameter of the
first micro-lens is set equal to or greater than 0.95 and less than
1.0.
9. A solid-state image sensor according to claim 4, wherein: the
greater curvature of the lens surface of the second micro-lens than
the curvature of the lens surface of the first micro-lens is set by
forming the second micro-lens in a circular shape in a plan view
and forming the first micro-lens in a rectangular shape in a plan
view.
10. A solid-state image sensor according to claim 4, wherein: the
greater curvature of the lens surface of the second micro-lens than
the curvature of the lens surface of the first micro-lens is set by
forming the second micro-lens in a polygonal shape with at least
eight sides in a plan view and forming the first micro-lens in a
polygonal shape with seven or fewer sides in a plan view.
11. A solid-state image sensor according to claim 1, wherein: the
light condensing position of the second micro-lens is adjusted
toward the micro-lens side relative to the light condensing
position of the first micro-lens by setting a greater refractive
index for a lens material constituting the second micro-lens than a
refractive index for a lens material constituting the first
micro-lens.
12. A solid-state image sensor according to claim 1, wherein: with
L1 representing a thickness of the micro-lens and L2 representing a
distance between the micro-lens and a light-receiving surface of a
pixel at which the micro-lens is disposed, a ratio L2/L1 is set to
different values for the first micro-lens and the second micro-lens
so that the light condensing position of the second micro-lens is
adjusted further toward the micro-lens side than the light
condensing position of the first micro-lens.
13. A solid-state image sensor according to claim 12, wherein: the
ratio L2/L1 for the second micro-lens is set equal to or greater
than 3.72 and equal to or less than 3.98.
14. An image-capturing device, comprising: a solid-state image
sensor according to claim 1; a photographic lens; an image forming
unit that forms image information based upon outputs from the
plurality of image-capturing pixels; and a focus detection unit
that executes focus detection through a split-pupil phase
difference method based upon outputs from the plurality of focus
detection pixels.
Description
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein
incorporated by reference: Japanese Patent Application No.
2007-265388 filed Oct. 11, 2007, US Provisional Patent Application
No. 60/960,747, Oct. 11, 2007, and Japanese Patent Application No.
2007-339754 filed Dec. 28, 2007.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state image sensor and an
image-capturing device equipped with the solid-state image
sensor.
2. Description of Related Art
Today, video cameras and electronic cameras often come equipped
with an AF (autofocus) function as a standard feature. Such a
camera normally includes a solid-state image sensor constituted
with a CCD or a CMOS. The solid-state image sensor includes a
plurality of pixels equipped with photoelectric conversion units
that generate signal charges in correspondence to the amount of
incoming light, disposed in a two-dimensional array. On-chip
micro-lenses are disposed on the light-entry side of the
photoelectric conversion units. The micro-lenses are disposed in
order to condense light that would otherwise enter pixel areas
Other than the photoelectric conversion units onto the
photoelectric conversion units and thus increase the amount of
light entering the photoelectric conversion units.
A single lens reflex electronic camera often includes a focus
detector adopting the split-pupil phase difference method, provided
as a separate unit in addition to the solid-state image sensor
engaged in the image-capturing operation so as to detect the
focusing state quickly. However, during the focus detection, no
subject light enters the image sensor and, for this reason, no live
view image display is provided on the compact monitor installed at
the rear side of the camera. While the live view image is
displayed, on the other hand, no subject light enters a focus
detector that detects the focusing state through the split-pupil
phase difference method. This means that focus detection cannot be
executed via the focus detector during live view image display.
While technologies whereby focus detection is executed through the
contrast detection method (peak method) based upon signals provided
from the solid-state image sensor have been proposed, focus
detection cannot be executed quickly through such a method. To
address this issue, Japanese Laid Open Patent Publication No.
2003-244712 and Japanese Laid Open Patent Publication No.
2006-261292 each disclose a solid-state image sensor that includes
built-in focus detection pixels to be used in focus detection
through the split-pupil phase difference method.
SUMMARY OF THE INVENTION
There is still an issue that must be addressed effectively in the
technologies in the related art described above whereby the
solid-state image sensor used in image-capturing operation includes
built-in focus detection pixels to be engaged in focus detection
through the split-pupil phase difference method, in that the level
of focus detection performance achieved via such a solid-state
image sensor is bound to be lower.
According to the 1st aspect of the present invention, a solid-state
image sensor comprises: a plurality of image-capturing pixels, each
equipped with a first micro-lens used to condense light; and a
plurality of focus detection pixels engaged in focus detection,
each equipped with a second micro-lens used to condense light; the
plurality of image-capturing pixels and the plurality of focus
detection pixels being disposed in a two-dimensional array. The
first micro-lens and the second micro-lens are formed so that a
light condensing position at which light is condensed via the
second micro-lens is set further toward a micro-lens side than the
light condensing position at which light is condensed via the first
micro-lens.
According to the 2nd aspect of the present invention, in the
solid-state image sensor according to the 1st aspect, it is
preferred that the plurality of image-capturing pixels and the
plurality of focus detection pixels each include a photoelectric
converter; the photoelectric converter of each of the plurality of
image-capturing pixels and the photoelectric converter of each of
the plurality of focus detection pixels are disposed on a single
plane; and the first micro-lens and the second micro-lens are
disposed on a single plane.
According to the 3rd aspect of the present invention, in the
solid-state image sensor according to the 1st aspect, it is
preferred that the plurality of image-capturing pixels and the
plurality of focus detection pixels each include a photoelectric
converter; the plurality of focus detection pixels each include a
light shield member with an opening formed therein; the light
shield member is disposed between the photoelectric converter and
the second micro-lens; and the light condensing position at which
light is condensed via the second micro-lens is set on a plane on
which the light shield member is disposed.
According to the 4th aspect of the present invention, in the
solid-state image sensor according to the 1st aspect, it is
preferred that the light condensing position of the second
micro-lens is adjusted toward the micro-lens side relative to the
light condensing position of the first micro-lens by setting a
greater curvature for a lens surface of the second micro-lens than
a curvature of a lens surface of the first micro-lens.
According to the 5th aspect of the present invention, in the
solid-state image sensor according to the 4th aspect, it is
preferred that the greater curvature of the lens surface of the
second micro-lens than the curvature of the lens surface of the
first micro-lens is set by setting a lens thickness of the second
micro-lens to be greater than a lens thickness of the first
micro-lens.
According to the 6th aspect of the present invention, in the
solid-state image sensor according to the 5th aspect, it is
preferred that, provided that a uniform lens diameter is assumed, a
ratio of the lens thickness of the second micro-lens and the lens
thickness of the first micro-lens is set equal to or greater than
1.1 and less than 1.4.
According to the 7th aspect of the present invention, in the
solid-state image sensor according to the 4th aspect, it is
preferred that the greater curvature of the lens surface of the
second micro-lens than the curvature of the lens surface of the
first micro-lens is set by setting a lens diameter of the second
micro-lens to be smaller than a lens diameter of the first
micro-lens.
According to the 8th aspect of the present invention, in the
solid-state image sensor according to the 7th aspect, it is
preferred that, provided that a uniform lens thickness is assumed,
a ratio of the lens diameter of the second micro-lens and the lens
diameter of the first micro-lens is set equal to or greater than
0.95 and less than 1.0.
According to the 9th aspect of the present invention, in the
solid-state image sensor according to the 4th aspect, it is
preferred that the greater curvature of the lens surface of the
second micro-lens than the curvature of the lens surface of the
first micro-lens is set by forming the second micro-lens in a
circular shape in a plan view and forming the first micro-lens in a
rectangular shape in a plan view.
According to the 10th aspect of the present invention, in the
solid-state image sensor according to the 4th aspect, it is
preferred that the greater curvature of the lens surface of the
second micro-lens than the curvature of the lens surface of the
first micro-lens is set by forming the second micro-lens in a
polygonal shape with at least eight sides in a plan view and
forming the first micro-lens in a polygonal shape with seven or
fewer sides in a plan view.
According to the 11th aspect of the present invention, in the
solid-state image sensor according to the 1st aspect, it is
preferred that the light condensing position of the second
micro-lens is adjusted toward the micro-lens side relative to the
light condensing position of the first micro-lens by setting a
greater refractive index for a lens material constituting the
second micro-lens than a refractive index for a lens material
constituting the first micro-lens.
According to the 12th aspect of the present invention, in the
solid-state image sensor according to the 1st aspect, it is
preferred that with L1 representing a thickness of the micro-lens
and L2 representing a distance between the micro-lens and a
light-receiving surface of a pixel at which the micro-lens is
disposed, a ratio L2/L1 is set to different values for the first
micro-lens and the second micro-lens so that the light condensing
position of the second micro-lens is adjusted further toward the
micro-lens side than the light condensing position of the first
micro-lens.
According to the 13th aspect of the present invention, in the
solid-state image sensor according to the 12th aspect, it is
preferred that the ratio L2/L1 for the second micro-lens is set
equal to or greater than 3.72 and equal to or less than 3.98.
According to the 14th aspect of the present invention, an
image-capturing device comprises: a solid-state image sensor
according to the 1st aspect; a photographic lens; an image forming
unit that forms image information based upon outputs from the
plurality of image-capturing pixels; and a focus detection unit
that executes focus detection through a split-pupil phase
difference method based upon outputs from the plurality of focus
detection pixels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram schematically illustrating the structure
of an electronic camera 1 achieved as an embodiment of the
image-capturing device according to the present invention;
FIG. 2 is a circuit diagram schematically illustrating the
structure of the solid-state image sensor 3;
FIG. 3 is a schematic plan view of the solid-state image sensor
3;
FIG. 4 is a schematic enlarged illustration of the pixel
arrangement assumed over an area where the focus detection areas 32
and 33 intersect each other;
FIG. 5 is a circuit diagram for 2.times.2 pixels 20 among numerous
pixels 20 disposed at the solid-state image sensor 3;
FIG. 6 presents a timing chart of an operation executed at the
solid-state image sensor 3;
FIGS. 7A, 7B and 7C respectively present a plan view, a sectional
view taken through X1-X1 and a sectional view taken through X2-X2,
each schematically illustrates the essential part of an
image-capturing pixel 20A;
FIGS. 8A and 8B respectively present a plan view and a sectional
view taken through X3-X3, each schematically illustrating the
essential part of an AF pixel 20B;
FIG. 9 illustrates light fluxes received at the AF pixel 20B
FIG. 10 illustrates the light fluxes received at an AF pixel 20B
assuming a structure in the related art;
FIG. 11 presents a list of methods that may be adopted in order to
alter the light condensing position;
FIG. 12 presents the results of optical simulations pertaining to
phase difference AF signal effectiveness factors, each
corresponding to one of three different types of micro-lenses
41;
FIG. 13 shows the relationship between the diameter ratio of the
micro-lens 41 and the phase difference AF signal effectiveness
factor ratio;
FIG. 14 shows the relationship between the thickness ratio of the
micro-lens 41 and the phase difference AF signal effectiveness
factor ratio;
FIG. 15 presents a plan view showing part of a solid-state image
sensor 3 that includes pixels 20B, at each of which a pair of
openings 44A and 44B corresponding to different pupil areas are
formed; and
FIG. 16 presents a graph indicating the L2/L1 dependency of the
phase difference AF signal effectiveness factor ratio.
DESCRIPTION OF PREFERRED EMBODIMENT
The following is a description of the best mode for carrying out
the present invention, given in reference to the drawings. FIG. 1
is a block diagram schematically illustrating the structure of an
electronic camera 1 achieved as an embodiment of the
image-capturing device according to the present invention. A
photographic lens 2, constituting an optical system via which an
image of a subject is formed, is mounted at the electronic camera
1. The photographic lens 2 includes a focusing lens and an aperture
which are driven by a lens control unit 2a. At the electronic
camera 1, a solid-state image sensor 3 at which the subject image
formed via the photographic lens 2 undergoes photoelectric
conversion is installed.
As the solid-state image sensor 3 is driven in response to a
command issued by an image-capturing control unit 4, electrical
signals corresponding to the subject image are output from the
solid-state image sensor. The signals output from the solid-state
image sensor 3 include image-capturing signals used to form image
signals representing the subject image and focus detection signals
used to detect the state of focus adjustment at the photographic
lens 2. It is to be noted that while the solid-state image sensor
may also output an exposure control signal, this signal does not
bear any relevance to the present invention and thus its
explanation is not provided.
The image-capturing signals and the focus detection signals are
processed at a signal processing unit and an A/D conversion unit 6,
and the signals having undergone the processing are temporarily
stored into a memory 7. The memory 7 is connected to a bus 8. The
lens control unit 2a, the image-capturing control unit 4, a
microprocessor 9, a focus calculation unit 10, a recording unit 11,
an image Compression unit 12, an image processing unit 13 and the
like are also connected to the bus 8. An operation unit 9a such as
a shutter release button is connected to the microprocessor 9. In
addition, a recording medium 11a is detachably loaded into the
recording unit 11, and data are recorded into the recording medium
11a and data in the recording medium 11a are reproduced via the
recording unit 11.
The focus detection signals having been stored into the memory 7 on
a temporary basis are then provided via the bus 8 to the focus
calculation unit 10. Based upon the focus detection signals, the
focus calculation unit 10 calculates the focus adjustment state,
determines the shift amount indicating the extent to which the
photographic lens 2 is to be driven and provides the value to the
lens control unit 2a. Namely, the focus calculation unit 10 outputs
a detection signal indicating the focus adjustment state to the
lens control unit 2a. The lens control unit 2a, in turn, adjusts
the focusing condition by driving the photographic lens 2 to a
specific position based upon the detection signal indicating the
focus adjustment state.
FIG. 2 is a circuit diagram schematically illustrating the
structure of the solid-state image sensor 3 in FIG. 1. The
solid-state image sensor 3 includes a plurality of pixels 20
disposed in a two-dimensional array and peripheral circuits through
which signals from the pixels 20 are output. Reference numeral 31
in FIG. 2 indicates an effective pixel area (image-capturing area)
where the pixels 20 are disposed in the two-dimensional array. The
pixels 20 will normally be disposed in a two-dimensional pattern
along two directions perpendicular to each other, e.g., the
longitudinal direction (columnar direction) and the lateral
direction (row direction). While FIG. 2 shows sixteen pixels 20 in
a four (lateral) row by four (longitudinal) row array to simplify
the illustration, the solid-state image sensor 3 in the embodiment
actually includes a far greater number of pixels than that shown in
FIG. 2. However, the present invention does not impose any
particular restrictions with regard to the number of pixels.
The solid-state image sensor 3 in the embodiment includes
image-capturing pixels 20A (see FIG. 4) that generate
image-capturing signals and focus detection pixels (hereafter may
be referred to as "AF pixels") 20B (see FIG. 4) that generate focus
detection signals (hereafter referred to as "AF signals"). However,
the pixels shown in FIG. 2 are assigned with reference numeral 20,
without distinguishing one type of pixel from the other. The
specific circuit structures and structural features of the various
types of pixels are to be described in detail later. A pixel 20
outputs an image-capturing signal or a focus detection signal in
response to a drive signal originating from a peripheral
circuit.
The peripheral circuits include a vertical scanning circuit 21, a
horizontal scanning circuit 22, drive wirings 23 and 24 connected
to the scanning circuits, vertical output lines 25 via which
electrical signals from the pixels 20 are received, constant
current sources 26 and correlated double sampling circuits (CDS
circuits) 27 connected to the vertical output lines 25, a
horizontal signal line 28 at which signals output from the
correlated double sampling circuits are received, an output
amplifier 29 and the like.
In response to a command issued by the image-capturing control unit
4 in the electronic camera 1, the vertical scanning circuit 21 and
the horizontal scanning circuit 22 output drive signals to the
drive wirings 23 and 24 respectively. Each pixel 20 is driven by a
drive signal from the vertical scanning circuit 21, taken in via a
specific drive wiring 23, and outputs an image-capturing signal or
an AF signal to the corresponding vertical output line 25. The
vertical scanning circuit 21 outputs a plurality of drive signals
and a plurality of drive wirings 23 are installed in
correspondence. It is to be noted that the drive wirings 23
connected to the vertical scanning circuit 21 are connected to the
gate electrodes of the MOS transistors disposed at the pixels. The
signals output from the pixels 20 undergo a specific type of noise
removal at the COS circuits 27 and are output to the outside via
the horizontal output line 28 and the output amplifier 29 based
upon drive signals provided from the horizontal scanning circuit
22.
FIG. 3 is a plan view schematically illustrating the solid-state
image sensor 3 (specifically its effective pixel area 31) in FIG.
1. As shown in FIG. 3, at the effective pixel area 31 of the
solid-state image sensor 3 in the embodiment, two focus detection
areas 32 and 33 located at the center and crossing each other, two
focus detection areas 34 and 35 located to the left and to the
right and two focus detection areas 36 and 37 located on the upper
side and on the lower side relative to the center of the effective
pixel area are set. However, the present invention is not limited
to this example. Focus detection areas may be set in a pattern
other than this or AF pixels may be cyclically and reiteratively
disposed over the entire effective pixel area 31, instead.
It is to be noted that an X axis, a Y axis and a Z axis extending
perpendicular to one another are defined as shown in FIG. 3. The
direction indicated by the arrow along the x-axis is referred to as
the +X direction or the +X side with the opposite direction
referred to as the -X direction or the -X side. The two opposite
directions running along the Y axis, too, are similarly referred
to. The XY plane is parallel with the image-capturing plane
(light-receiving surface) of the solid-state image sensor 3. The
pixels 20 are set side-by-side in rows that extend along the x-axis
and in columns that extend along the y-axis. It is to be noted that
incoming light from the photographic lens 2 enters from above the
drawing sheet on which FIG. 3 is drawn and advances downward into
the figure. This arrangement also applies to later drawings.
FIG. 4 schematically illustrates how pixels are arranged over an
area where the focus detection areas 32 and 33 in FIG. 3 intersect
each other in an enlarged view. While the solid-state image sensor
3 includes a single type of image-capturing pixels 20A and 4 types
of AF pixels 20B with different light-receiving areas, where the
incoming light is received, defined therein, the following
description is applicable to all types of AF pixels unless
specially noted.
Each pixel 20 includes disposed therein a photoelectric conversion
unit 42 and a micro-lens 41, via which the incoming light is guided
to the photoelectric conversion unit 42. It is to be noted that
while the photoelectric conversion units at the AF pixels 20B
assume a shape identical to that of the photoelectric conversion
units 42 at the image-capturing pixels 20A, FIG. 4 shows a light
shield film 43 with an opening 44 disposed over the photoelectric
conversion unit instead of the photoelectric conversion unit at
each AF pixel 20B. Depending upon the position of the opening 44,
the area over which the incoming light is guided to the
photoelectric conversion unit of the AF pixel 20B is defined.
FIG. 5 is a circuit diagram pertaining to a pixel area with
2.times.2=4 pixels 20 present therein, which includes part of the
focus detection area 33 at the solid-state image sensor 3
constituted of numerous pixels 20. Namely, FIG. 5 presents a
circuit diagram pertaining to two AF pixels 20B and two
image-capturing pixels 20A. The pixels 20 (the image-capturing
pixels 20A and the AF pixels 20B) in the embodiment all assume
identical circuit structures. Each pixel 20 is constituted with a
photoelectric conversion unit (photo diode) 42 at which an
electrical charge corresponding to the incoming light is generated,
a floating diffusion 52 that takes in and accumulates the
electrical charge, a pixel amplifier transistor 53 that outputs a
signal corresponding to the potential at the floating diffusion 52,
a transfer transistor 51 that transfers the electrical charge from
the photoelectric conversion unit 42 to the floating diffusion 52,
are set transistor 55 that resets the voltage at the floating
diffusion 52 and a selector transistor 54 via which the particular
pixel 20 is selected.
As described above, the pixels 20 each include a plurality of
transistors via which the electrical signal corresponding to the
electrical charge is generated and output. Such a circuit structure
assumed at the pixels 20 is a standard circuit structure for pixels
each constituting a structural unit in a CMOS solid-state image
sensor.
The transfer transistor 51, the pixel amplifier transistor 53, the
reset transistor 55 and the selector transistor 54 in the
embodiment are each constituted with an NMOS transistor. The
floating diffusion 52 is actually constituted with an n-type
impurity semiconductor region FD formed at a p-type silicon
substrate, an internal wiring electrically connecting the FD to the
gate electrode of the pixel amplifier transistor 53 and the gate
electrode of the pixel amplifier transistor 53.
It is to be noted that the gate electrodes of the transfer
transistors 51 at the individual pixels 20 in each pixel row in
FIGS. 2 and 5 are commonly connected to a drive wiring 23, and a
drive signal OTX is provided from the vertical scanning circuit 21
to the pixels 20 in the particular row via the drive wiring 23. The
gate electrodes of the selector transistor 54 at the individual
pixels 20 in each pixel row are commonly connected to the
corresponding drive wiring 23 and a drive signal OSEL is provided
to the pixels from the vertical scanning circuit 21 via the drive
wiring 23. The gate electrodes at the reset transistors 55 at the
individual pixels 20 in each row are commonly connected to the
corresponding drive wiring 23 and a drive signal ORES is provided
to the pixels from the vertical scanning circuit 21 via the drive
wiring 23. The drive wirings 23 connected to the vertical scanning
circuit 21 are laid out so that they extend along the row direction
(X direction) parallel to one another.
FIG. 6 presents a timing chart of an operation executed at the
solid-state image sensor 3. Through the operation shown in the
timing chart, the image-capturing signals and the AF signals are
output in units of individual rows. However, only the AF signals
may be output by specifically selecting only the AF pixels in the
focus detection area.
Prior to a time point t1 in FIG. 6, the drive signal ORES sustains
high level and the reset transistors 55 remain in an ON state. The
floating diffusions 52 are thus reset to a reference level (e.g.,
the dark level). At the time point t1, the drive signal ORES is
switched to low level. As a result, the reset transistors 55 enter
an OFF state and the reset level of the floating diffusions 52 are
sustained in the OFF state In addition, the drive signal OSEL for
the row to be selected (the first row in FIG. 6) is switched to
high level and the selector transistors 54 are set to the ON state
at the time point t1. Thus, the individual pixels in the selected
row become connected to the corresponding vertical output lines 25
and electrical charges corresponding to the reference level signals
output from the floating diffusions 52 are output and accumulated
into the CDS circuits 27 from the pixel amplifier transistors 53
via the vertical signal lines 25.
At a time point t2, the drive signal OTX is switched to high level.
Then at a time point t3, the drive signal OTX is reset to low. As a
result, the electrical charges having accumulated at the
photoelectric conversion units 42 are transferred to the floating
diffusions 52, and signals that include the electrical charge
signals superimposed on the reference level signals are output to
the CDS circuits 27 from the pixel amplifier transistors 53 via the
vertical output lines 25. Subsequently, image signals and AF
signals, obtained via the CDS circuits 27 by determining the
differences between the most recently output signals and the
earlier reference level signals, are output.
At a time point t4, the drive signal OSEL is set to low level and
the selector transistors 54 are turned off. As a result, the
connection between the individual pixels 20 in the selected row and
the corresponding vertical output lines 25 becomes cut off.
Subsequently, the next row (second row) is selected and image
signals and AF signals are output with the drive signals for the
various transistors controlled at time points t1' through t4' in a
similar manner. The image signals or AF signals having been read
out first undergo a specific type of processing and then are stored
into the memory 7. If focus detection processing needs to be
executed, the AF signals are read out from the memory 7 and a
specific type of processing is executed on the AF signals. When an
image is to be brought up on display, the image signals read out
from the memory 7 undergo specific processing.
FIGS. 7A, 7B and 7C respectively present a plan view, a sectional
view taken along X1-X1 in FIG. 7A and a sectional view taken along
X2-X2 in FIG. 7A, each schematically illustrating the essential
part of an image-capturing pixel 20A. The image-capturing pixel 20A
includes the photoelectric conversion unit 42 and an on-chip
micro-lens 41 formed over the photoelectric conversion unit 42.
While various layers, including a color filter, are formed between
the micro-lens 41 and the photoelectric conversion unit 42, they
are not shown in FIGS. 7A.about.7C.
As shown in FIGS. 7A.about.7C, the micro-lens 41 assumes a
rectangular shape in a plan view (see the shape of the micro-lens
41 in the plan view), the curvature of a curved micro-lens surface
S2 in the X2-X2 section is smaller than the curvature of a curved
micro-lens surface S1 in the X1-X1 section taken along the diagonal
direction. The light condensing position P1 at which light is
condensed via the micro-lens 41 of the image-capturing pixel 20A is
either right on a light-receiving surface 42A or closer to the
substrate 45 relative to the light-receiving surface 42A. In the
example presented in FIGS. 7B and 7C, the light condensing position
P1 is assumed at a point closer to the substrate 45 relative to the
light-receiving surface 42A. The center of the photoelectric
conversion unit 42 and the center of the micro-lens 41 are aligned
with each other and thus, a light flux from an exit pupil area,
which is not substantially offset from the center of the exit pupil
of the photographic lens 2, is received and undergoes the
photoelectric conversion at the photoelectric conversion unit 42 of
the image-capturing pixel 20A.
FIGS. 8A and 8B respectively present a plan view and a sectional
view taken along X3-X3 in FIG. 8A, each showing the essential part
of an AF pixel 20B. FIGS. 8A and 8B show a pixel among the AF
pixels 20B disposed in the focus detection area 32 in FIG. 4, at
which the incoming light is received on the left side of the
optical axis. The same reference numerals are assigned to
components identical to or corresponding to those in FIGS.
7A.about.7C and the following explanation focuses on elements
different from those in FIGS. 7A.about.7C.
A light shield film 43 is disposed between the micro-lens 41 and
the photoelectric conversion unit 42 at the AF pixel 20B, and one
of the two split light fluxes, separated from each other through
pupil splitting, enters the photoelectric conversion unit 42,
unblocked by the light shield film 43. In addition, the micro-lens
41 assumes a circular shape in a plan view, as shown in FIG. 8A,
and the micro-lens diameter is set smaller than that of the
micro-lens 41 in FIG. 7A assuming a rectangular shape in the plan
view. Thus, as long as the height of the micro-lens 41 (the
micro-lens thickness) is set equal to that of the micro-lens 41 at
the image-capturing pixel 20A in FIGS. 7B and 7C, the curvature of
the micro-lens curved surface S3 is greater than either of the
curvatures of the curved surfaces S1 and S2 shown in FIGS. 7B and
7C. This means that the light condensing position P2 at which light
is condensed via the micro-lens 41 at the AF pixel 20B is further
toward the micro-lens than the light condensing position P1 of the
micro-lens 41 in the image-capturing pixel 20A. In the embodiment,
the light condensing position P2 is set at a point substantially
matching the position assumed by the light shield film 43.
The light shield film 43, disposed on the light-entry side of the
AF pixel 20B, defines the area over which the incoming light enters
the photoelectric conversion unit 42. More specifically, an opening
44 is formed at the light shield film 43 and this opening 44
defines the area over which the incoming light enters the
photoelectric conversion unit 42. The opening 44 is formed on the
-X side relative to the optical axis O (see FIG. 8B) of the
micro-lens 41. Thus, a light flux from an exit pupil area
substantially offset toward the +X side relative to the center of
the exit pupil of the photographic lens 2 is selectively received
to undergo photoelectric conversion at the photoelectric conversion
unit 42.
It is to be noted that since the micro-lens disposed at the AF
pixel 20B and the micro-lens disposed at the image-capturing pixel
20A assume shapes identical to each other in the related art, the
light condensing position P2 of the AF pixel 20B and the light
condensing position P1 of the image-capturing pixel 20A are exactly
the same. In other words, light decentered toward the opposite
side, too, enters the AF pixel 20B in the related art. At the
solid-state image sensor 3 in the embodiment, however, the signal
component decentered to the opposite side is reduced (to be
described in detail later).
Likewise, among the AF pixels 20B shown in FIG. 4, an AF pixel 20B
with an opening 44 formed on the right side (the +X side) of the
optical axis selectively receives a light flux from an exit pupil
area offset toward the -X side from the center of the exit pupil,
an AF pixel 20B with an opening 44 formed on the upper side (the +Y
side) of the optical axis selectively receives a light flux from an
exit pupil area offset toward the -Y side from the center of the
exit pupil and an AF pixel 20B with an opening 44 formed on the
lower side (the -Y side) of the optical axis selectively receives a
light flux from an exit pupil area offset toward the +Y side from
the center of the exit pupil.
The focus calculation unit 10 that executes focus detection through
the split-pupil phase difference method calculates a defocus amount
indicating an extent of defocusing through correlation operation
executed based upon AF signals from a plurality of AF pixels 20B
that receive light fluxes from the exit pupil area offset toward
the +X side and AF signals from a plurality of AF pixels 20B that
receive light fluxes from the exit pupil area offset toward the -X
side. It also executes focus detection based upon AF signals from a
plurality of AF pixels 20B that receive light fluxes from the exit
pupil area offset toward the +Y side and AF signals from a
plurality of AF pixels 20B that receive light fluxes from the exit
pupil area offset toward the -Y side.
It is crucial to detect light fluxes from the exit pupil areas
assuming positions symmetrical to each other relative to the
optical axis by clearly distinguishing those departing one exit
pupil area from those departing the other, so as to assure highly
accurate focus detection through the split-pupil phase difference
method. At the same time, better image-capturing performance via
each image-capturing pixel 20A must be assured by setting the light
condensing position at which light is condensed via the micro-lens
41 to a point on the light-receiving surface or closer to the
substrate However, solid-state image sensors in the related art are
not configured by taking this into consideration and instead,
micro-lenses 41 assuming identical shapes are optimal for
image-capturing operation, are disposed both at the image-capturing
pixels 20A and the AF pixels 20B. Thus, the focus detection
accuracy cannot be maximized.
In the solid-state image sensor 3 achieved in the embodiment, the
two requirements described above are satisfied by assuming
different light condensing positions for the micro-lenses 41 at the
image-capturing pixels 20A and the AF pixels 20B. Namely, the light
condensing position P1 is set for each image-capturing pixel 20B at
a point close to the light-receiving surface (more specifically,
right on the light-receiving surface 42A or a point further toward
the substrate 45 relative to the light-receiving surface 42A, as
shown in FIG. 7B and 7C) optimal for the image-capturing operation,
whereas the light condensing position P2 is set for each AF pixel
20B at a position on the light shield film 43 further toward the
micro-lens relative to the light-receiving surface, so as to
reliably ensure that only one of the two split light fluxes,
separated from each other through pupil splitting, is received.
FIG. 9 illustrates light fluxes received at an AF pixel 20B. In
FIG. 9, the light fluxes drawn with horizontal stripes are the
light fluxes that enter the light-receiving surface, whereas the
light fluxes without stripes indicate light fluxes that do not
reach the light-receiving surface. In addition, each light flux on
the right side of a one-point chain line is a light flux advancing
from the exit pupil area offset to the right (toward the +X side)
from the center of the exit pupil, whereas each light flux on the
left side of the one-point chain line is a light flux advancing
from the exit pupil area offset to the left (toward the -X side)
from the center of the exit pupil. The light fluxes from the
left-side exit pupil area are all blocked at the light shield film
43 and only the light fluxes having advanced from the right-side
exit pupil area enter the photoelectric conversion unit 42. As a
result, accurate focus detection can be executed through the
split-pupil phase difference method.
FIG. 10 shows an AF pixel 20B in the related art. The AF pixel in
the related art includes a light shield film 43 disposed at a pixel
structured identically to the image-capturing pixel 20A described
earlier. The image-capturing pixel 20A assumes a light condensing
position P1 set toward the substrate and near the light-receiving
surface, so as to assure desirable image-capturing characteristics.
However, if the same pixel is used as an AF pixel simply by
disposing a light shield film 43, as shown in FIG. 10, light fluxes
from the left-side exit pupil area, too, pass through the opening
44 and enter the photoelectric conversion unit 42 since the light
condensing position P1 is near the light-receiving surface. In
addition, there are light fluxes advancing from the right-side exit
pupil area, which are blocked at the light shield film 43. As a
result, the phase difference AF performance is bound to be
compromised in the related art.
At the solid-state image sensor 3 in the embodiment, different
optimal positions at which light is condensed via the micro-lenses
41, are assumed for the image-capturing pixels 20A and the AF
pixels 20B, so as to assure desirable image-capturing
characteristics and desirable AF characteristics at the same
time.
It is to be noted that while the micro-lenses 41 at the
image-capturing pixels 20A assume a rectangular shape, identical to
the shape of the pixels in the plan view, and the micro-lenses at
the AF pixels 20B assume a circular shape in the plan view in the
embodiment described above, the micro-lenses at the pixels may
assume shapes other than these. Namely, when micro-lenses with a
uniform thickness are used, the curvature of a micro-lens curved
surface can be increased, so as to set the light condensing
position P2 of the AF pixel 20B further toward the micro-lens than
the light condensing position P1 set for the image-capturing pixel
20A. For instance, the micro-lens 41 at the AF pixel 20B may assume
a polygonal shape with at least eight sides in the plan view, very
close to a circular shape, whereas the micro-lens 41 at the
image-capturing pixel 20A may assume a polygonal shape with fewer
than eight sides in the plan view.
Methods commonly adopted when forming on-chip micro-lenses 41
include the reflow method (see, for instance, Japanese Patent No.
2604890) and the etch-back method (see, for instance, Japanese
Patent No. 2776810). For instance, a convex micro-lens 41,
achieving curvatures such as those shown in FIG. 7, can be formed
through the reflow method by heating a rectangular-patterned
micro-lens material (thermoplastic resin) and thus thermally
deforming the micro-lens material. By using a micro-lens material
patterned with equilateral hexagonal shapes instead of rectangles,
micro-lenses 41 assuming an equilateral hexagonal shape in the plan
view can be obtained.
The circular micro-lens 41 at the AF pixel 20B in FIGS. 8A and 8B,
on the other hand, can be obtained by reflowing a
circular-patterned micro-lens material. It is to be noted that
since micro-lenses 41 are formed through thermal deformation of the
micro-lens material, the rectangular micro-lenses 41 do not
actually achieve a perfectly rectangular shape. Instead they assume
a shape with rounded corners in the plan view. Micro-lenses 41
described to assume a rectangular shape in the plan view may
actually have rounded corners or beveled corners. This allowance is
applicable when micro-lenses 41 assume another polygonal shape as
well.
While different light condensing position P1 and P2 are assumed by
altering the shape of the micro-lens in the plan view in the
embodiment described above, the light condensing position may be
adjusted through a method other than this. For instance, different
light condensing positions may be set for micro-lenses assuming
identical shapes and identical sizes in the plan view simply by
altering the micro-lens thickness. Alternatively, different light
condensing positions may be set for micro-lenses assuming identical
shapes (e.g., circular) in the plan view and equal micro-lens
thicknesses, i.e., for micro-lenses assuming identical shapes,
simply by altering the diameter. As a further alternative, the
light condensing positions may be adjusted by using micro-lens
materials with varying refractive indices, instead of altering the
shapes of the micro-lenses. Micro-lens materials with varying
refractive indices may be phenol positive photoresist that contains
naphthoquinone diazide as the photosensitive group (to be used in
the reflow method, or silicon oxide or silicon nitride (to be used
in the etch-back method).
FIG. 11 presents a list of the methods that may be adopted to
adjust the light condensing position as described above. Assuming
that the micro-lenses all have identical shapes in the plan view,
the light condensing position P2 of the AF pixel 20B can be
adjusted towards the micro-lens by increasing the micro-lens
thickness. When the micro-lenses assume the uniform thickness, on
the other hand, the light condensing position P2 of the AF pixel
20B can be adjusted toward the micro-lens side by reducing the
micro-lens diameter or by increasing the refractive index of the
micro-lens material.
When one of the two split light fluxes, separated from each other
through pupil splitting, is received through the opening 44 formed
at the light shield film 43, the desirable position at which the
light is condensed is the position P2 on the light shield film 43,
as described earlier. As the light condensing position is set apart
from the position P2 by a greater extent, the performance level of
the phase difference AF executed based upon the signal output from
the photoelectric conversion unit 42 becomes lower. FIG. 12
presents the results of optical simulations of phase difference AF
performance levels (each represented by a phase difference AF
signal effectiveness factor) corresponding to three different types
of micro-lenses 41.
The phase difference AF signal effectiveness factor may indicate a
value calculated by, for instance, allowing light fluxes advancing
from the exit pupil area offset to the right (toward the +X side)
from the exit pupil center, as shown in FIG. 9 to enter an AF pixel
20B (see FIG. 4) with the opening 44 thereof offset to the left
relative to the optical axis, as shown in FIG. 9 to detect the
right-side light fluxes and also to enter an AF pixel 20B (see FIG.
4) with the opening 44 thereof offset to the right relative to the
optical axis to detect the left-side light fluxes and determining
the intensity ratio of the detection signals indicating the
intensity levels of the light fluxes having entered the AF pixels.
Namely, the phase difference AF signal effectiveness factor assumes
a value in proportion to (output from the right-side light flux
detection pixel 20B) (output from the left-side light flux
detection pixel 20B). When the phase difference AF signal
effectiveness factor assumes a greater value, a higher level of
phase difference AF performance is achieved.
The value of the ratio (output from the right-side light flux
detection pixel 20B)/(output from the left-side light flux
detection pixel 20B), calculated in conjunction with the AF pixels
assuming a light condensing position identical to that of the
image-capturing pixels 20A, as shown in FIG. 10, is now considered.
As explained earlier, the light fluxes drawn with horizontal
stripes reach the light-receiving surface, whereas the non-striped
light fluxes are blocked at the light shield film 43 and thus do
not enter the light-receiving surface. In this situation, some of
the right-side light fluxes that should be detected at the
right-side light flux detection pixel 20B shall be blocked at the
light shield film 43, which reduces the value assumed for the
numerator in the phase difference AF signal effectiveness factor,
ultimately reducing the phase difference AF signal effectiveness
factor. In addition, as shown in FIG. 10, light fluxes (left-side
light fluxes) advancing from the pupil area on the opposite side,
which should not enter the right-side light flux detection pixel at
all, shall enter the pixel. This means that right-side light fluxes
also enter the left-side light flux detection pixel 20B. As a
result, the denominator in the phase difference AF signal
effectiveness factor increases to result in smaller value assumed
for the phase difference AF signal effectiveness factor. Thus, if
the light condensing position is the same as that assumed for the
image-capturing pixels 20A, as shown in FIG. 10, the phase
difference AF signal effectiveness factor is reduced.
The results of the optical simulations (optical condition set for
the photographic lens 10: F2.8 (on-axis), AF pixel condition:
micro-lenses assume a circular shape in the plan view) presented in
FIG. 12 indicate that the phase difference AF signal effectiveness
factor calculated in correspondence to the micro-lens structure
ideal for image-capturing, such as that shown in FIG. 10, assumed a
small value of 4.3. When the opening diameter at the micro-lens 41
is reduced by 10% without altering the micro-lens thickness, the
micro-lens curved surface assumes a greater curvature and the light
condensing position moves toward the micro-lens from the point P1
in FIG. 10, improving the phase difference AF signal effectiveness
factor to 10.9. In addition, by increasing the micro-lens thickness
by 10% without altering the micro-lens diameter, the phase
difference AF signal effectiveness factor is increased to 9.7,
achieving better phase difference AF performance over that achieved
in the structure shown in FIG. 10.
FIG. 13 shows the relationship between the diameter ratio of the
micro-lens 41 at an AF pixel 20B and the phase difference AF signal
effectiveness factor ratio. Each ratio takes on a relative value
representing the ratio of the value corresponding to the micro-lens
41 at the AF pixel to the value corresponding to of the micro-lens
at the image-capturing pixel 20A. When the micro-lens diameter
ratio is equal to or greater than 0.95 and less than 1.0, the phase
difference AF signal effectiveness factor ratio is greater than
1.0, indicating an improvement in the phase difference AF
performance over the related art. FIG. 14 shows the relationship
between the micro-lens thickness ratio and the phase difference AF
signal effectiveness factor ratio. When the micro-lens thickness
ratio is set equal to or greater than 1.10 and less than 1.40, the
phase difference AF signal effectiveness factor ratio assumes a
value equal to or greater than 2, achieving a greater extent of
improvement in the phase difference AF performance over that
achieved by altering the diameter of the micro-lens 41, as shown in
FIG. 13. Accordingly, this may be regarded as the ideal approach to
be taken in conjunction with the micro-lens at the AF pixel
20B.
It is to be noted that the light condensing position may be
adjusted even more effectively by using a lens material with a
greater refractive index to constitute the micro-lens 41 at the AF
pixel 20B, as well as adjusting the diameter or the thickness of
the micro-lens 41. It shall also be obvious that the light
condensing position may be adjusted through a combination of these
means.
In the embodiment described above, the light condensing position of
the AF pixel 20B is adjusted toward the micro-lens by altering the
diameter, the thickness or the refractive index of the micro-lens
41. However, simply by adjusting the distance L2 between the lower
end of the micro-lens 41 and the light-receiving surface of the
photoelectric conversion unit 42 shown in FIG. 9, the light
condensing position can be shifted without having to alter the
shape or material of the micro-lens 41. Since the light condensing
position is also affected by the micro-lens thickness L1, as
explained earlier, a specific L2/L1, which shall optimize the
micro-lens 41 for the AF pixel 20B, can be determined.
FIG. 16 presents the results of simulations related to the L2/L1
dependency of the phase difference AF signal effectiveness factor
ratio. It is to be noted that the phase difference AF signal
effectiveness factor ratio in FIG. 16 is calculated in reference to
the phase difference AF signal effectiveness factor of a micro-lens
41 that would assure the optimal autofocus performance, e.g., the
phase difference AF signal effectiveness factor of a micro-lens 41
that would assure a phase difference AF signal effectiveness factor
ratio of 2 in FIG. 14. In addition, the simulations are conducted
in conjunction with a micro-lens (with a circular shape in the plan
view) identical in shape to that used in the image-capturing pixel
20A.
The simulation results presented in FIG. 16 indicate that when
L2/L1 is equal to or greater than 3.72 and equal to or less than
3.98, the phase difference AF signal effectiveness factor ratio is
equal to or greater than 1, achieving the optimal autofocus
performance. Namely, when the micro-lens 41 has a shape identical
to that of the micro-lens at the image-capturing pixel 20A, L2/L1
should be set equal to or greater than 3.72 and equal to or less
than 3.98. While FIG. 16 presents the results of simulations
related to a micro-lens assuming a specific shape, a micro-lens
with another shape shall demonstrate similar L2/L1 dependency and
thus, shall indicate a similar phase difference AF signal
effectiveness actor ratio. It is to be noted that since better AF
sensitivity is assured with a micro-lens 41 with a greater
diameter, the micro-lens 41 should assume a diameter close to the
size of the pixel itself.
As explained above, the light condensing position can also be
adjusted by altering the distance L2 between the lower end of the
micro-lens 41 and the light-receiving surface of the photoelectric
conversion unit 42 in FIG. 9. Accordingly, the distance between the
lower end of the micro-lens 41 and the light-receiving surface of
the photoelectric conversion unit 42 may take on different values
at the image-capturing pixel 20A and the AF pixel 20B. In addition,
by shifting the light condensing position of the AF pixel 20B
toward the micro-lens through adjustment of the diameter, the
thickness or the refractive index of the micro-lens 41, the
micro-lens 41 of the image-capturing pixel 20A and the micro-lens
41 of the AF pixel 20B can be disposed on a single plane.
In the embodiment described above, the light condensing position P1
of the micro-lens 41 at the image-capturing pixel 20A is set near
the light-receiving surface as in the related art whereas the light
condensing position P2 of the micro-lens 41 at the AF pixel 20B is
adjusted further toward the micro-lens by altering the shape of the
micro-lens 41 in the plan view, the thickness of the micro-lens 41
or the like. As a result, the AF performance through the
split-pupil phase difference method is improved and desirable
image-capturing performance and desirable AF performance are
assured at the same time.
It is to be noted that an explanation is given above in reference
to the embodiment on an example in which the present invention is
adopted in the solid-state image sensor 3, which includes AF pixel
20B each having an opening 44 thereof set on the left side and AF
pixels 20B each having an opening 44 thereof set on the right side
to be paired up with a left-side opening, alternately disposed
along the X direction. However, the present invention is not
limited to this example and may be adopted equally effectively in a
structure that includes AF pixels 20B each having a pair of
openings 44A and 44B corresponding to different pupil areas. The AF
pixels 20B in such a structure should include photoelectric
conversion units each corresponding to one of the openings 44A and
44B, so that AF signals corresponding to the two openings 44A and
44B are output without interfering with each other. Furthermore,
the present invention may be adopted in an image-capturing device
such as a video camera that executes focus detection by calculating
the defocus amount, instead of an electronic camera.
The above described embodiments are examples, and various
modifications can be made without departing from the scope of the
invention.
* * * * *